For the purpose of future isolation by isotachophoresis of activated hGH isohormones D and E in amounts sufficient for growth assay in man, pilot studies were conducted aiming at the determination of (a) yield of enzymatic digestion with plasmin and yield of isotachophoresis; (b) maximal load capacity compatible with sufficient resolution; (c) the effect of lyophilization of the final product on bioactivity in the rat tibia assay; (d) the effect of aging of the lyophilized products on bioactivity. Clinical assay protocols were formulated. Digestion with subtilisin-B gives rise to a product distinct from hGH-E. hPRL from amniotic fluid was found to have a highly charged component appearing as "big" on gel filtration. BIBLIOGRAPHIC REFERENCES: Skyler, J.S., Baumann, G., and Chrambach, A.: A Catalogue of isohormones of human growth hormone based on quantitative polyacrylamide gel electrophoresis. Acta Endocr. Suppl., 211:1-40, 1977. Skyler, J.S., Chrambach, A., and Li, C.H.: Quantitative polyacrylamide gel electrophoresis and specific activities of human somatroipin and its derivatives. Biochim. Biophys. Acta, 491: 566-572, 1977.